1. Field of the Invention
The present invention relates generally to reinforced molding resins. More particularly, this invention describes reinforced polycarbodiimide modified polyalkylene terephthalate molding resin compositions.
2. Summary of the Prior Art
Polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate resins were first disclosed in U.S. Pat. No. 2,465,319 to Whinfield and Dickson.
Recent investigations with reinforced polypropylene terephthalate and polybutylene terephthalate molding resins have indicated that they are surprisingly superior to similarly reinforced polyethylene terephthalate in many important processing and performance characteristics. For example, polypropylene terephthalate and polybutylene terephthalate may be molded and processed at lower temperatures, have a shorter cycle time in the mold, and do not require, as does polyethylene terephthalate, the presence of either a nucleating agent or an internal mold release agent. Furthermore, reinforced polypropylene terephthalate and polybutylene terephthalate molding resins have correspondingly higher tensile strength, lower water absorption and better creep (flexural) properties than does similarly reinforced polyethylene terephthalate.
As a direct result, these polypropylene terephthalate and polybutylene terephthalate molding resins have been found to solve processing problems long associated with polyethylene terephthalate and believed by those skilled in the art to be equally associated with all polyalkylene terephthalates. Equally as significant, these molding resins present a noticeably improved balance of performance properties which those skilled in the art did not believe to exist as evidenced by the extensive use of polyethylene terephthalate molding resins to the almost total exclusion of other polyalkylene terephthalates.
Consequently, the superior processing requirements and physical properties of the polypropylene terephthalate and polybutylene terephthalate molding resins makes them more commercially desirable, with a wider area of applicability than polyethylene terephthalate.
Reinforced polypropylene terephthalate and polybutylene terephthalate resins are also well known in the art. For example, U.S. Pat. No. 3,814,725, which is assigned to the assignee of the present invention, discloses improved thermoplastic polyester molding resins comprising a reinforcing filler and a polypropylene terephthalate or a polybutylene terephthalate polymer. These molding resins have filled a long existing need in providing outstanding molding processing advantages combined with outstanding physical properties of the molded articles. U.S. Pat. Nos. 3,751,396 and 3,783,349, also assigned to the assignee of the present invention, disclose flame retardant reinforced polybutylene terephthalate or polypropylene terephthalate polymers with similar processing advantages and property advantages as those thermoplastic molding resins described in U.S. Pat. No. 3,814,725.
It is also known to add carbodiimides to polyesters for various purposes. See, e.g., U.S. Pat. Nos. 3,193,522; 3,193,523; 3,193,524; and 3,835,098. For example, U.S. Pat. No. 3,193,522 discloses a process for stabilizing polyesters against hydrolytic degradation by adding polycarbodiimides to the polyesters. The polycarbodiimides must have a molecular weight of at least 500 and have more than three carbodiimide groups in the molecule with the provision that at least one carbodiimide group be present for each molecular weight unit of 1500. The polycarbodiimides may be aliphatic, aromatic, unsubstituted, or highly substituted. In that patent, there is no disclosure or suggestion that the use of any particular polycarbodiimides of the broad class disclosed will increase the impact strength of reinforced polyesters necessary in order to render them useful for certain molding applications, especially in molding articles of manufacture for certain automotive, industrial, or electrical applications where increased impact strength may extend the life of such articles.
Also, U.S. Pat. Nos. 3,193,523 and 3,193,524 disclose the use of monocarbodiimides to stabilize polyesters. Furthermore, U.S. Pat. No. 3,835,098 discloses the reaction of intermediate molecular weight thermoplastic elastomeric copolyesters with minor amounts of a polycarbodiimide in order to provide compositions which exhibit properties similar to those exhibited by copolyesters having a higher degree of polymerization.
Co-pending U.S. patent application Ser. No. 715,946 (N. W. Thomas, F. M. Berardinelli, and R. Edelman), which was filed on Aug. 19, 1976, and is assigned to the assignee of the present invention, generically discloses and claims a process for preparing certain polycarbodiimide modified thermoplastic polyesters. The modified thermoplastic polyesters have increased melt strength and are suitable for extrusion applications. This process comprises incorporating into the structure of a thermoplastic saturated polyester having at least one carboxyl end group, at least one polycarbodiimide which polycarbodiimide both (a) is derived from at least one aromatic diisocyanate which is either unsubstituted or contains up to one methyl substituent on each aromatic ring, and (b) contains at least three carbodiimide units per polycarbodiimide molecule by reacting the carboxyl end group of the polyester while in the molten state with the carbodiimide group of the polycarbodiimide.
The resulting polycarbodiimide modified thermoplastic polyesters have increased melt strength and intrinsic viscosity and a decreased number of carboxylic acid end groups. These improved melt strength polyesters also have improved die swell characteristics and are useful in extrusion applications such as blow molding.
Co-pending U.S. patent application Ser. No. 768,528, now U.S. Pat. No. 4,052,360, entitled "Reinforced Flame Retardant Polyester Composition Having Non-Drip Characteristics," (F. M. Berardinelli and R. Edelman), which was filed on Feb. 14, 1977, and which is also assigned to the assignee of the present invention, discloses and claims a process for preparing a reinforced flame retardant copolyester molding resin composition having non-drip characteristics. This process comprises intimately mixing
A) at least one reinforcing agent PA1 B) at least one Group Vb metal-containing compound, and PA1 C) the molten reaction product of PA1 (2) at least one polycarbodiimide, which polycarbodiimide both PA1 (a) is derived from at least one aromatic diisocyanate which is either unsubstituted or contains up to one methyl substituent on each aromatic ring, and PA1 (b) contains at least two carbodiimide units per polycarbodiimide molecule
(a) at least one alkane diol having from two to six carbon atoms selected from the group consisting of ethylene glycol, 1,3-propane diol, 1,4-butane diol, 1,5-pentane diol, and 1,6-hexane diol, PA2 (b) terephthalic acid, isophthalic acid, or a dialkyl ester thereof wherein the alkyl radical contains from 1 to 7 carbon atoms, and PA2 (c) a halogenated derivative of the bishydroxyethylether of p,p'-isopropylidenediphenol, having the formula ##STR1## wherein the aromatic nuclei of the p,p'-isopropylidenediphenol are substituted with from one to four halogen atoms, R is a bivalent hydrocarbon radical containing from 2 to 6 carbon atoms, m and n are integers from 1 to 10, and the halogenated derivative of the bishydroxyethylether of p,p'-isopropylidenediphenol comprises from about 8 to about 40% by weight of the copolyester composition, PA2 (a) is derived from at least one aromatic diisocyanate which is either unsubstituted or contains up to one methyl substituent on each aromatic ring, and PA2 (b) contains at least three carbodiimide units per polycarbodiimide molecule,
and
whereby the resulting reinforced copolyester molding resin composition is flame retardant and exhibits non-drip characteristics.
However, none of these patents or patent applications which disclose stabilizing or otherwise modifying polyesters by reacting them with carbodiimides, suggests that the resulting modified polyesters have the improved impact strength necessary in order to be useful for certain molding applications, especially in molding articles of manufacture for certain automotive, industrial, or electrical applications where increased impact strength may extend the life of such articles which may be subjected to occasional or continuous shock or impact.